Seismic exploration operations generally utilize a seismic energy source to generate an acoustic signal that propagates into the earth. The acoustic signal is partially reflected by subsurface seismic reflectors in the earth, which may include interfaces between subsurface lithologic or fluid layers that may be characterized by different elastic properties. The reflected signals are detected and recorded by seismic receiver units (hereinafter, ‘nodes’) located at or near the surface of the earth, thereby generating a seismic survey of the subsurface environment. The recorded signals, or seismic energy data, can then be processed to yield information relating to the lithologic subsurface formations, identifying such features as, for example, lithologic subsurface formation boundaries.
Generally, the method for detection and recording of seismic signals is similar on land and in marine environments; however, marine environments present unique challenges presented by the body of water overlying the earth's surface. Seismic exploration operations in marine environments are typically conducted from the deck of one or more seismic exploration vessels, such as floating platforms or ships. The seismic exploration vessels typically provide storage and transportation for a plurality of nodes and associated operational equipment. Seismic exploration in deep water typically involves the deployment of nodes from the deck of the seismic exploration vessel and their placement on or near the bottom of a body of water.
As shown and described in U.S. Pat. No. 7,933,165 (the '165 patent), the subject matter of which is incorporated herein by reference in its entirety, FIG. 1A is a schematic side view of a deployment operation from a vessel 5 using a (load-bearing, non-signal-transmitting) cable 1. In the deployment operation, the cable 1 is paid out over a backdeck 10 of the vessel 5 from a spool, sheave or pulley, powered or otherwise, such as a cable handling device 15. The cable 1 includes a plurality of connectors 20 that must pass through at least a portion of the cable handler 15. A seismic sensor unit (‘node’) 25 is coupled to each of the respective connectors 20 as the cable passes over the backdeck 10 by personnel onboard the vessel. In the deployment operation, the nodes 25 are coupled to the connectors 20 by a lanyard 30, which may be a length of flexible rope, cable, or chain. The cable with nodes 25 coupled thereto form a mainline cable that falls to rest on or near a bottom 40 of a body of water 35 to form at least a portion of a seismic array. The mainline cable may be many miles long and have over 200 nodes attached. After one or more mainline cables are positioned on the bottom 40 to assist in lowering the nodes to the bottom 40, the seismic survey is performed.
Referring again to the '165 patent, FIG. 1B is a perspective view of a portion of the (load-bearing, non-signal-transmitting) cable 1 prior to coupling with nodes 25 of FIG. 1A. Each of the connectors 20 typically include a body 45 that is larger than the diameter of the cable, and is configured to clamp or fasten to an outer surface of the cable. The connectors 20 include ring-like or hook-like members 50 to facilitate connection and disconnection of the nodes. The cable also includes a plurality of discrete cable coupling devices 55 configured to connect ends of cable sections to increase the overall length of the cable. After the seismic survey, the cable and nodes are retrieved. During retrieval, the cable is spooled or routed through a winch, reel or sheave, a pinch roller powered or otherwise, for example, the cable handler 15 of FIG. 1A, which pulls the cable and nodes from the water. As the cable passes over the deck of the vessel, the nodes are detached from the cable and the cable and nodes are stowed.
As the cable 1 shown in FIGS. 1A and 1B may be routed through a cable handler during deployment and/or retrieval, the connectors 20 and/or cable coupling devices 55 pose a risk of snagging, binding, or tangling the cable. In some cases, the ring-like or hook-like members 50 protrude from the periphery of the body 45, which may snag, bind, or tangle the cable. Further, the ring-like or hook-like members 50 create the risk of injury to personnel that may be in the vicinity of the cable, such as during node coupling and decoupling. Still further, in rough seas or merely during the node deployment and/or recapture operations, the lanyard may become pinched at the point of connection to the connector, resulting in entanglement or disconnection and loss of one or more nodes.
FIG. 1C (FIG. 7A of the '165 patent) is a perspective view of a cable connector 715, which includes a rotatable clamp 700 disposed on a central coupling section 225. The rotatable clamp 700 includes a swivel portion 705 and an attachment ring 710 coupled by a neck 725. The swivel portion 705 is configured to be positioned within a circumferential groove in the connector and is rotatable relative to the groove and/or the connector 715. The attachment ring 710 is configured as an attachment point for a node or a node tether and/or a clamp device as described in the '165 patent. As shown, the attachment ring 710 is shaped as a D-ring and includes a gap 720 to define a split ring. The outer dimension of the swivel portion 705 is substantially circular and defines a diameter that is equal to or slightly smaller than an outer diameter of the central coupling section 225 of the connector.
The inventors have recognized the advantages and benefits of a practical and robust solution directed to solving the problems and addressing the shortcomings in the art described above and others known in the art.